Optical analysis of a semiconductor electrooptic modulator with microstrip electrode

Abstract

This work presents the optical analysis of a semiconductor electrooptic modulator with microstrip electrode on a GaAs substrate. Prior to optical analysis, microwave analysis by using the finite element method is carried out. In MATLAB environment, Laplace‟s equation is solved to obtain the potential distribution over the cross section of the active region of the optical modulator, where the cross section is discretized into Lagrange triangular elements and appropriate Dirichlet type boundary conditions is applied on the shielding wall and on the electrodes. When the potential of each and every node is known then capacitance is calculated by energy formula, and hence the microwave properties are calculated. The electric field in each element is calculated from potential of each node of the element and then anisotropic change in refractive index due to electrooptic effect is determined. With the new refractive index, the optical analysis is carried out using full-wave vector finite element method with the edge/nodal hybrid element. Effects of various waveguide parameters of the modulator, such as the waveguide width, the electrode width, the core height, the buffer thickness, and the Aluminium concentration of the buffer layers on the optical properties such as the half-wave voltage length product etc. are thoroughly investigated. The effects are investigated with special emphasis on velocity and impedance matching, so that higher bandwidth can be achieved. The obtained results are also compared with some published data and correlated agreement was obtained for both microwave properties and optical properties. It has also been found that dielectric loss of the modulator plays an important role on the maximum attainable bandwidth of the modulator.